Thermionic tube and circuits for the same



April 1932- F. s. MCCULLOUGH 1,853,281

THERMIONIC TUBE AND CIRCUITS FOR THE SAME Filed Jan. 5; 1926 INVENTOR Patented A r; 12,1932.

UNITED? STATES FREDERICK S. McCULLOUGH,'OF EDGEWOOD, PENNSYLVANIA THEBMIONIG TUBE AND Application filed January This inventionrelatesto thermionic tubes 7 and to circuits therefor, and more particularly to a tube and circuit of the indirectly heated cathode, type. o

It has heretofore been proposed to provide radio tubes having a relatively large cathode area wherein the cathode is general-' preciable potential gradient along the cathode, as there is in the usual hot filament cathode type of tube. V

For this. reason, such tubes in operation have a rather large grid current, which is not always desirable, and the characteristics, of

the tube are not the same as the characteristics of a tube of the hot filament cathode ccording to the present invention, it is proposed to provide a tube of the indirectly heated cathode type, wherein means is provided for impressing different potentials at different points on the cathode, so as to render it non-equi-potential, whereby the characteristics of the tube may be more readily controlled, and the magnitude of the grid currents effectively reduced without requiring excessively high biasing batteries.

The invention may be readily understood by reference to the accompanying drawing which illustrates diagrammatically one embodiment of the invention, it being understood that the drawing is diagrammatic, and merely illustrative of one embodiment of my I invention, and that various changes and modifications are within the contemplation thereof. 7

In the drawing: The figure represents diagrammatically a 5 thermionic tube embodying the invention and a portion of a circuit therefor.

Referring to the drawing, 2 designates a suitable envelope which may be evacuated, and within which is a plate electrode or anode 3, a control electrode 4, and a cathode struccrncuirs roe THE SAME 5, 1926; Serial No. 79,353.

ture designated generally as 5. The cathode structure includes a cathode member 6, which is preferably of cylindrical form and which may have a surface coating of a suitable material, adapted to sustain electron emission at relativelylow operating temperatures. YVithin the cylindrical cathode member 6 is a suitable heater wire 7. This heater wire may be raised to incandescence, or to suitable temperature by means of an alternating or a direct current applied across the terminals thereof, accordingto theusual practice with tubes of this type. Connected with one end of the cathode member 6 is alead wire'8, which is connected with the plate electrode 3 through a suitable so'urcefof a direct current potential, such as the B battery 9. This battery has its negative pole connected to the cathode in the usual manner, and its positive pole connected with I the plate Connected with the opposite end of thec'athode member 6 is'a second lead wire 10, which may be connected with the grid or control electrode 4: through a control battery 11. The battery 11 will preferably have its positive side connected with the cathode 6 and its negative side connected with the grid.

It will thus be seen that the battery 11 applies a positive potential at one end of the cathode while the battery 9 applies a negative potential at'the other end thereof, whereby the cathode 6 is rendered non-equi-potential.

With an arrangement as thus described, the cathode is effectually rendered non-equipotential, and the tube may, inoperation, ap-

proach more nearly the characteristics of av tube of the hot filament type.

By proper adjustment of the potential at 11, the operation of the tube may be controlled, and with the arrangement as thus i provided, the magnitude of the grid current maybe decreased or .its efiect minimized, without excessively large biasing voltages.

I claim as my invention:

1. In an electric circuit, a thermionic tube having a plate, a grid and an elongatedv cathode of the indirectly heated type, a source of current having its positive pole connected to the plate and its negative pole connected to one end of the cathode, and a Hit" second source of direct current having its positive pole connected to the opposite end of said cathode and its negative pole connected to the grid.

2. In a vacuum tube circuitemploying a vacuum tube having an elongated indirectly heated cathode, a grid and a plate, a con nection between the plate and one end of the cathode including a source of direct current, a connection between the grid and the other end of the cathode, said connection includ ing a source of direct current the polarity of which is reversed as regardsthecathode, with respect to the first.

3. The combination with a thermionic tube of the indirectly heated cathode type having an elongated cathode structure and having a plate electrode, of a plurality of direct cur rent sources connected to the cathode at separated points and so arranged as to cause a current flow of small magnitude along the cathode during the operation ofthe tube to thereby render the cathode non-equi-potential.

4. A thermionic tube having an elongated cathode, a heating means associated therewith within the tube and also having a control and plate electrode, a source ofdirect cur rent connected across one end of the cathode and the plate, and a second source of direct current connecting the opposite end of the cathode with the control electrode, the said second source of direct current having its polarity reversed With respect-to the first.

In testimony whereof I have hereunto set my hand.

FREDERICK S. MCCULLOUGH. 

